Field of the Invention
The present disclosure generally relates to determining the amount of liquid within a tank, and more particularly to sensor arrangements and systems for determining the height of liquid within tanks such as tanks containing liquefied propane gas.
Description of the Related Art
For as long as small portable propane tanks have been around, inventors have been trying to find low cost and reliable methods to accurately measure the propane level in the tank. There have been many attempts to provide a solution to this problem, but all have various short-comings whether it is inaccuracy, reliability, or cost. Various techniques have been developed which fall into one of the following categories:
One way to determine the amount of liquid in a tank is to correlate the temperature difference between the liquid and the gas in an attempt to determine the propane level. However, these techniques may not provide very good accuracy or resolution and may require that the connected appliance be in use in order to function.
There are devices that utilize pressure in the tank that attempt to tell a user when the tank is getting low. As an example, some two-stage regulators used on recreational vehicles (RV) use this type of device, which typically includes a color coded diaphragm indicator that indicates when a tank is running low based on the sensed pressure in the tank. The problem is that these types of pressure devices can be difficult for the normal consumer to use because pressure in the tank can vary greatly depending on the temperature of the tank, and further, pressure changes occur as gas flows from the tank during use. So predicting an exact pressure at which one could say a tank is running low can be difficult, and it can be even more difficult to determine the exact propane level based on these pressure-sensing devices.
There are devices that use the tank weight as the indicator of gas level, but as anyone in the tank exchange business could attest to, there are millions of tanks in circulation, with some being over 50 years old. Thus, tare weights of tanks vary greatly, making this type of device inaccurate. Further, some weight measuring devices that fit under the tank are not useable because there are space constraints in the appliance or RV that make it impossible to fit. Some weight measuring devices are also built into grills and use spring-loaded mechanisms to hang the tank, but obviously these are only useable on that grill, and after some time in the weather many don't work well due to corrosion.
There are more expensive tanks that have been developed with built in visual gauges that operate off a float located within the tank. These tanks can work well to measure the propane level; however, they can be relatively costly. They can also be confounded by the practice of swapping tank via tank exchange services instead of refilling and retaining an instrumented tank. Purchasing such a tank becomes useless because the customer cannot use these exchange services, and normal refilling services are becoming harder and harder to find, and almost never open on the weekends or outside normal business hours.
There are devices in the consumer market that use ultrasonic pulse to detect propane level, but they are single point application devices that must be held to the side of the tank and give a simple red or green light indicating whether liquid propane was detected at the location they are held. Therefore, they must be used at multiple locations each time to determine an actual level. A key factor in making ultrasonic technology functional can be the ‘coupling’ of the ultrasonic device to the wall of the tank so that accurate signals are transmitted and received correctly. Due to the human interaction required to push these devices onto the wall of the tank, the ‘coupling’ can vary greatly and these types of devices therefore may not able to repeat their indications well. For example, the first use might give a red light, and repeated right away give a green light. Thus, it can end up being an exercise to find the fluid line, taking numerous measurements rapidly up and down the tank, until finally feeling confident in where the fluid line may be located.
Similarly, there are ultrasonic devices used on large propane tanks, 200 gallons and up, that use an ultrasonic sensor to determine tank level. However these systems require very strong ultrasonic transducers, thus requiring a likewise large battery. They are connected via wire harness to a transmitter box that must be mounted on the top side of the tank unobstructed. The transmitter box then communicates only with the manufacturer's satellite system that in turn communicates via the internet to a customer. Given the size of the system, complexity, and cost of over $1000, it is not a viable alternative for the portable propane tanks.
While each of these devices may have certain limited applications, there remains a need for improved sensor arrangements, sensor systems, and methods for determining height of liquid in tanks. The present disclosure provides a solution to this need.